As part of Operation Fast and Furious, agents were told to forego immediate arrests of suspected straw purchasers of guns and instead try to track the guns to higher-ups in gun-smuggling rings. Such a tactic is normally barred under Justice Department policy.

Agents lost track of hundreds of guns that flowed south to Mexico, where many were recovered at crime scenes. Two such guns were found in the U.S. at the scene of the killing of border agent Brian Terry.

Holder told the committee he became aware of the gun-walking tactic at the same time as the public and that he found out “about the same time” that guns found at the scene of Terry's death were part of Operation Fast and Furious.

Holder has faced off repeatedly with Darrell Issa of California and other Republicans in recent months over his handling of the aborted firearms investigation. Issa's House Oversight and Government Reform Committee has prepared a contempt citation against Holder but not voted on it yet, applying pressure for more documents on Operation Fast and Furious.

Holder said the Justice Department has cooperated fully with congressional investigators and turned over 7,600 pages of material to Congress about the operation.

“Look, I don't want to hear about the 7,600,” snapped Issa, who has been Holder's frequent sparring partner during recent gun-walking hearings.

Issa said Thursday that wiretap applications in Operation Fast and Furious indicate that a number of key individuals at the Justice Department were responsible for the use of the gun-walking tactic.

“I've read them,” replied Holder, adding that he disagreed with Issa's conclusions. The material on the wiretaps is sealed in a federal court, but Issa said the committee obtained the applications from whistleblowers cooperating with his investigation.

Gun-walking has long been barred by Justice Department policy but was used in the Arizona operation in an effort to dismantle entire arms-trafficking networks and reach kingpins who had long eluded prosecution.